1. Field of the Invention
The present invention relates to the selective removal of acetylenic compounds from hydrocarbon streams using specific Ni-based catalysts and the process of making the catalysts. The process is particularly useful in cleaning up MAPD (methyl acetylene and propadiene) and acetylene in crude mixed olefin streams or phenylacetylene in crude styrene streams by selective hydrogenation in the presence of the Ni-based catalyst.
2. Related Information
Acetylenic impurities such as acetylene, methyl acetylene, vinyl acetylene, ethyl acetylene, and 2-methyl-1-buten-3-yne are found in various crude mixed C2-C5 streams, for example in the manufacture of olefins such as ethylene, propylene, butadiene and isoprene. These acetylenic impurities need to be removed with a minimum loss of the useful olefinic materials, i.e., ethylene, propylene, butenes, butadiene, isoprene and the like.
For example, 1,3-butadiene is an important raw material used to produce various polymers such as butadiene-styrene copolymer. One of the processes for producing 1,3-butadiene is co-production of various olefins by steam cracking of petroleum fractions. The crude mixed C4 stream from a steam cracker is selectively hydrogenated to partially remove C4 acetylenic compounds. The selectively hydrogenated stream is sent to the 1,3-butadiene recovery unit where solvent extractive distillation techniques are used to separate 1,3-butadiene from the rest of components in the mixed stream. Solvent extractive distillation is expensive to operate and energy consumption is intensive.
Complete removal of C4 acetylenic compounds in the stream with high recovery of 1,3-butadiene is highly desirable to reduce the production cost of 1,3-butadiene and produce a premium quality product for polymer production. However, formerly it was technically impossible to completely remove C4 acetylenes in crude mixed streams by selective hydrogenation without unacceptably high loss of 1,3-butadiene due to over-hydrogenation of 1,3-butadiene. Therefore, an improved inexpensive process via a highly active and selective catalyst is highly desirable to produce premium quality 1,3-butadiene without paying a penalty for high loss of 1,3-butadiene due to over-hydrogenation.
The preferred technique for the purification in commercial practice is the selective hydrogenation of acetylenic compounds over hydrogenation catalysts. Supported Pd, Ni, Cu and Co catalysts are known as useful for the hydrogenation of acetylenes (Handbook of Commercial Catalysts, pp. 105-138, Howard F. Rase, CRC Press, 2000). The most preferred catalysts in prior commercial applications of selective hydrogenation of acetylenes are palladium-based catalysts such as Pd, Pd/Pb, Pd/Ag or Pd/Au on a support such as alumina and the copper catalysts on a support such as alumina. Pd catalysts were the most preferred catalysts because of high activity and higher selectivity compared with other known metal catalysts.
However, palladium-based catalysts are not selective enough to completely remove C4 acetylenes without an unacceptable amount of 1,3-butadiene loss due to over-hydrogenation. Another inherent problem of palladium-based catalysts is the loss and migration of palladium due to the formation of soluble Pd complex compounds by the reaction of Pd atoms on the catalyst surface with vinyl acetylene, if the hydrogenation is carried out with a liquid phase. Silver and gold have been used to minimize the loss of palladium and reduce catalytic polymerization of acetylenic compounds.
The copper-based catalysts are very selective so that the recovery of 1,3-butadiene from the mixed stream is very high compared with palladium-base catalysts. The activity of copper catalysts is very low compared with palladium-based catalysts, and a large volume of catalyst and large reactor are required. Also because the deposition of heavy carbonaceous materials on the catalyst occurs quickly, frequent regeneration of catalysts necessitates multiple reactors.
Ni catalysts in any form are very active catalysts for selective hydrogenation of acetylenes and dienes. According to R. S. Mann et al. (Can. J. Chem. 46, p. 623, 1968), Ni and Ni—Cu alloy catalysts are effective for methyl acetylene hydrogenation. The catalytic activity rapidly increases with addition of copper to nickel up to 25 wt. % in alloy catalyst. The selectivity to propylene and extent of polymerization increase with the increase of copper in the alloy. Nickel-based catalysts have been used in commercial processes for the selective hydrogenation of acetylenic impurities in mixed steams of olefins and diolefins.
Despite recent improvements made in the performance of catalysts, still further improvement is desired for the selective hydrogenation of acetylenic compounds in a C2 or C3 mixed olefin stream to improve selectivity, activity and catalyst cycle time for the production of large volume olefins such as propylene and ethylene. For the commercial production of large volume commodities, such as propylene, even small improvements in selectivity of MAPD to propylene or catalyst activity is highly desirable.